Emergency shelters are structures built for residence and dwelling during or after a manmade or natural disaster, such as a fire, flood, tornado or earthquake. In some disasters such as tornadoes, survival depends heavily on the mechanical strength and quality of the emergency shelters. Temporary emergency shelters available on the market that are adaptable to individual use, such as inexpensive tents, lack the necessary strength, durable quality, and environmental conformability for survival during a natural disaster. Emergency shelters that overcome some of the disadvantages of temporary shelters are often built primarily for other purposes, such as schools, churches, gymnasiums, etc. They are more expensive and difficult to build, are not practical to be owned by a family, and are sometimes not available at a near distance to a person in need of survival during a disaster situation.
A spherical ball or a round ball is a three dimensional object that has a spherical surface, characterized as a perfectly round geometrical object in a three-dimensional space. A spherical surface has a set of points that are all the same distance, which is referred to as the radius of the sphere or r, from a given point in space. The given point is known as the center of the sphere. The shortest path connecting two points lying entirely in the sphere is a minor arc of the great circle passing the points. On a sphere, a central angle of an arc of a great circle is an angle spanned by the radii from each end of the arc to the center of the sphere. A plane section of a sphere is a circle. A great circle, also known as an orthodrome or Riemannian circle, of a sphere is the intersection of the sphere and a plane which passes through the center point of the sphere, as opposed to a general circle of a sphere where the plane is not required to pass through the center. A sphere may be divided into two equal hemispheres by any plane that passes through its center.
A spherical ball is unique in many ways. For instance, in comparison to other three dimensional objects, a spherical ball has the largest volume for the smallest surface area: the sphere has the smallest surface area among all surfaces enclosing a given volume and it encloses the largest volume among all closed surfaces with a given surface area.
For the reason above, a building structure made in resemblance to a sphere may have the benefit of lower consumption of construction materials, lower cost, more enclosed space for use, higher structural strength and better safety. Such a structure that resembles a hemisphere or the hollow upper half of a sphere is often referred to as a dome. Dome structures made of various materials have a long architectural lineage. Their prevalence in use has resulted in many types and variations, such as an onion dome, corbel dome, geodesic dome, oval dome, polygonal dome, sail dome, saucer dome, umbrella dome, etc.